A body in free space has six independent degrees of freedom, three translational, and three rotational, all typically defined with respect to a Cartesian coordinate system with the three translational degrees of freedom taking place along the three perpendicular axis of the Cartesian coordinate system, and the three angular degrees of freedom being defined as rotational degrees of freedom about the axis of the same system. The motion of a body in space can be described as a linear combination of these coordinates. In general each degree of freedom can be restrained with the appropriate placement of a point restraint on the body. A nearly ideal point restraint can be achieved using a high quality hardened steel ball bearing pressing against a polished sapphire plate that is optically flat (better than 0.25 microns) that is attached to the body being constrained. Within the field of opto-mechanical design the concept of a “kinematical design” is well known, here the designer is challenged to provide just one nearly ideal constraint for each of the six degrees of freedom that a body has in free space. Additionally a successful kinematic design is typically considered to be relatively independent of the structure being built but relies on the use of inexpensive mass produced parts such as precision hardened steel ball bearings and small optically polished sapphire plates to form a kinematic interface between moving or joined parts. The book “Building Scientific Apparatus” by John H. Moore et al describes the details of achieving a reasonable approximation to a kinematic design, see for example page 43 sections 1.6.1 and 1.6.2 of the 3rd addition. Here the authors describe how to achieve a kinematic design such that the resulting devices can be used in the very demanding application of optical assemblies where motion between parts of a fraction of a wavelength of light can be deleterious to the operation of the device. One such example is provided by Moore et al in FIG. 1.44 wherein a two plate kinematic device is illustrated, the device is designed to allow the two plates to come together stably such that the two plates when combined and lightly loaded together exhibit no extraneous motion between them. A number of companies sell opto-mechanical devices based on the principles thought by Moore et al, one such company is Thorlabs Inc of Newton N.J., their Kinematic Base Plate part number KB3X3 found in the Volume 19 version of the Thorlabs product catalog.
This KB3X3 device is advertised as providing micro-radian level repeatability in its rotational degrees of freedom after repeated removal and replacement of the top of the two part device. It is assumed that the bottom part of the device is securely fixed to a massively rigid structure, typically an optical table also sold by Thorlabs. The typical use of the Thorlabs device is to allow the user to build flexible optical systems with one use being the redirecting of a laser beam on an optical table from one experimental setup to another with a high degree of repeatability. To achieve this function a KB3X3 in located along the laser beam path, for this example assume an existing experiment lies a small distance in front of the source of the laser beam. Utilizing a kinematic mirror mount for example a Thorlabs KS1 along with an appropriate mirror, the mirror is mounted to the top plate of the KB3X3 using opto-mechanical holders well known within the field of optical sciences and also provided by Thorlabs. Once the mirror is appropriately affixed to the KB3X3 such that it redirects the laser beam, the user would then use the mirror mount controls to deflect the beam well away from the uninterrupted beam path to an unused portion of the optical table. Now the user can have the laser available for two experiments, by placing the top plate of the KB3X3 onto its base the beam is deflected precisely along the desired path to the unused portion of the optical table where a second experiment can be constructed. And by removing the top plate of the KB3X3 the undeflected beam is free to travel past the KB3X3 to serve the first application.
Various optical instruments require precise alignment of at least one optical element relative to another as discussed above, where the alignment tolerance determines the accuracy and precision of the instrument's measurements. One example of such an instrument is a SH Wavefront Sensor. SH Wavefront Sensors are capable of accurate measurements of an optical wave front's shape and intensity distribution by analyzing the location and intensity of spots (spot field) formed by imaging an incident light field onto a CCD (charge coupled device) camera, for example, via a lenslet array or a micro-lens array. To achieve sufficient measurement precision and accuracy, the lenslet array must be very precisely aligned relative to the CCD sensor. Typically the lenslet array is permanently fixed relative to the CCD to assure precise alignment over time. This limits the measurement to a maximum wave front slope, determined primarily by the pitch of the micro-lens array and the effective focal length of the micro-lens array. There would be a tremendous benefit to being able to change the micro-lens array in the field without requiring the user to perform a calibration procedure, while maintaining the measurement accuracy and precision of a SH sensor with a “fixed” micro-lens array.